Overview
This section provides general steps to follow if you observe undesirable system conditions. Follow the
steps listed until you solve the problem. Some of the items are system specific. We reference the section
in this manual of more information is available. Always observe the safety precautions listed in the
Introduction section and any precautions related to your specific equipment.
System Operating Hot
Item
Description
Action
Oil level in reservoir.
Insufficient hydraulic fluid does not meet
cooling demands of system.
Fill reservoir to proper level.
Heat exchanger.
Heat exchanger is not sufficiently cooling
the system.
Check air flow and input air temperature
for heat exchanger. Clean, repair or
replace heat exchanger.
Bypass valve
Leakage through by-pass line with high speed operation
may cause temperature increase
Inspect bypass valve and replace as necessary. Check that
bypass valve is tightened.
System relief pressure
settings
If the system relief valves are worn, contaminated, or valve
settings are too low, the relief valves get overworked.
Verify settings of high pressure relief valves
and adjust or replace as necessary.
System pressure.
Frequent or long term operation over system relief setting
creates heat in system.
Measure system pressure. If pressure
is too high, reduce loads.
Transmission Operates Normally in One Direction Only
Item
Description
Action
Control linkage
Control linkage is operating improperly.
Repair/replace linkage
Interchange charge check/
HPRVs
Interchanging the charge check/HPRVs will show if the
problem is related to the valve function.
If the problem changes direction, replace the defective
valve.
Bypass valve is open
Open bypass valve will cause either direction to be
inoperative
Close/repair bypass function
System will not Operate in Either Direction
Item
Description
Action
Oil level in reservoir
Insufficient hydraulic fluid to supply system loop.
Fill reservoir to proper level.
Bypass valve is open
If bypass valve is open, the system loop becomes
depressurized.
Close bypass valve
Charge pressure with pump
in neutral
Low charge pressure insufficient to recharge system loop
Measure charge pressure with the pump in neutral. If
pressure is low, go to next step.
System pressure
Low system pressure does not provide enough power to
move load.
Measure system pressure. Continue to next step.
Charge check/HPRVs
Low system pressure does not provide enough power to
move load.
Repair or replace charge check/HPRVs
Control linkage
Linkage operating improperly.
Repair/replace linkage
Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Troubleshooting
©
Danfoss | June 2021
AX152886481311en-000304 | 19
